The erosion control properties of arbuscular mycorrhizal fungi in a restoration context: A test of site-specific native and commercially available amendments

Background/Question/Methods

Slopes constructed from unconsolidated soil used as fill pose special challenges to restoration practitioners. Denuded slopes are prone to erosion prior to and during vegetation establishment. Arbuscular mycorrhizal fungi (AMF) have been shown to improve the establishment and growth of many plant species, and commercial cultures of AMF are widely used as soil amendments throughout the restoration industry. Native AMF have also been shown to influence plant establishment and growth, in both negative and positive ways. Both commercially available and native AMF contribute to the structure and functioning of naturalized plant communities, and in the rhizosphere, hyphal growth is known to influence the stabilization of soil into aggregates.  It is not known, however, whether the benefits of reduced soil erosion can be attributed directly to AMF or to the interactions of AMF and their host plants.  It is also not known whether field application methods influence the efficacy of AMF in erosion control. In a one-year field experiment in a California grassland, we investigated the soil-holding properties of two mycorrhizal amendments cultured in a greenhouse: a commercially available product and a native mycorrhizal community originating from soil specific to an undisturbed area of the restoration site. Both treatments were compared to an autoclaved control inoculum. We applied these treatments using one of two methods: as dry inoculum raked into test plots, or as a slurry applied hydraulically in a bonded fiber matrix from hydromulching equipment.  We used a 2 X 3 full factorial randomized block design replicated 5 times. All plots received a common seed mix and a clean, hydraulically applied bonded fiber matrix. Catchment basins at the base of each test plot allowed soil and water harvests to be quantified.
Results/Conclusions

After one very dry growing season, soil loss estimates suggest commercially available and native mycorrhizal communities can reduce soil erosion, but native AMF cultures yield less sediment overall. Hydraulically applied treatments complement these microbial effects by further reducing sediment yield. These results suggest AMF applications in general and site-specific AMF in particular can be useful as erosion control tools in revegetating filled embankments.